Bounty Material Mask

It creates random colors all of your object materials in the scene and copy them to another scene. Use rendered image for postprocessing by selecting different materials easily.

http://www.yafaray.org/community/forum/viewtopic.php?f=13&t=4787&hilit=+passes

From Condar:

Material ID: change all materials in your scene to Shiny Diffuse with Emit=1, choose hideous colours for every material, remove all lights, render with Direct Lighting WITHOUT AO, three or four render passes with 2 AA samples per pass and threshold=0.003.

Script sets 4 AA passes instead of 2.